The corneal epithelium activity transports both amino acids and ions. These active transport processes are dependent upon the presence of extracellular Na ion. Active amino acid transport is stimulated by low concentrations of lactate, ascorbate and GSSG. Transport is inhibited by 6-aminonicotinamide, CO and HOONO but it is not inhibited by iodoacetate, rotenone, cyanide or 2,4-dinitrophenol. It has been shown that ascorbate and GSSG play a role in the regulation of the hexose monophosphate shunt which is extremely active in the corneal epithelium. We will examine hexose monophosphate shunt activity, ATPase activity, ATP levels and GSSG/GSH levels under conditions that influence amino acid transport. These studies should give us insight into the role of the hexose monophosphate shunt and Na ion plus K ion - ATPase in control of active transport by the corneal epithelium.